Fix timestamp frequency mismatch in idle timeout calculation

Copilot · eiriktsarpalis · Copilot · commit 01982ebd8103 · 2025-12-15T19:45:55.000Z
Convert TimeSpan.Ticks to timestamp ticks using TimeProvider.TimestampFrequency.
TimeSpan.Ticks uses 100-nanosecond intervals (10,000,000 per second), but
TimeProvider.GetTimestamp() returns ticks based on TimeProvider.TimestampFrequency,
which varies by platform (e.g., ~1,000,000,000 on macOS, ~10,000,000 on Windows).

This was causing IdleTimeout to be incorrectly calculated, resulting in sessions
timing out much faster than configured on platforms with different frequencies.

Co-authored-by: eiriktsarpalis &lt;2813363+eiriktsarpalis@users.noreply.github.com&gt;
diff --git a/src/ModelContextProtocol.AspNetCore/StatefulSessionManager.cs b/src/ModelContextProtocol.AspNetCore/StatefulSessionManager.cs
@@ -18,9 +18,18 @@ internal sealed partial class StatefulSessionManager(
 
     private readonly TimeProvider _timeProvider = httpServerTransportOptions.Value.TimeProvider;
     private readonly TimeSpan _idleTimeout = httpServerTransportOptions.Value.IdleTimeout;
-    private readonly long _idleTimeoutTicks = httpServerTransportOptions.Value.IdleTimeout.Ticks;
+    private readonly long _idleTimeoutTicks = GetIdleTimeoutInTimestampTicks(httpServerTransportOptions.Value.IdleTimeout, httpServerTransportOptions.Value.TimeProvider);
     private readonly int _maxIdleSessionCount = httpServerTransportOptions.Value.MaxIdleSessionCount;
 
+    private static long GetIdleTimeoutInTimestampTicks(TimeSpan idleTimeout, TimeProvider timeProvider)
+    {
+        // Convert TimeSpan.Ticks (100-nanosecond intervals) to timestamp ticks based on TimeProvider.TimestampFrequency.
+        // TimeSpan.Ticks uses a fixed frequency of 10,000,000 ticks per second (100ns intervals).
+        // TimeProvider.GetTimestamp() returns ticks based on TimeProvider.TimestampFrequency, which varies by platform
+        // (e.g., ~1,000,000,000 on macOS using nanoseconds, ~10,000,000 on Windows using 100ns intervals).
+        return (long)(idleTimeout.Ticks * timeProvider.TimestampFrequency / (double)TimeSpan.TicksPerSecond);
+    }
+
     private readonly object _idlePruningLock = new();
     private readonly List<long> _idleTimestamps = [];
     private readonly List<string> _idleSessionIds = [];
